1. Field of the Invention
This invention is concerned with a process for converting synthesis gas, i.e., mixtures of gaseous carbon oxides with hydrogen or hydrogen donors, to hydrocarbon mixtures and oxygenates. In one aspect, this invention is concerned with a process to convert such synthesis gas to hydrocarbon mixtures under conditions permitting good temperature control of the known exothermic reduction of carbon monoxide with hydrogen. In still another aspect, this invention is concerned with providing a novel catalyst system for conversion of synthesis gas to valuable hydrocarbon products rich in the valuable lower olefins ethylene and propylene.
2. Prior Art
Processes for the conversion of coal and other hydrocarbons such as natural gas to a gaseous mixture consisting essentially of hydrogen and carbon monoxide, or of hydrogen and carbon dioxide, or of hydrogen and carbon monoxide and carbon dioxide, are well known. Although various processes may be employed for the gasification, those of major importance depend either on the partial combustion of the fuel with an oxygen-containing gas or on a combination of these two reactions. An excellent summary of the art of gas manufacture, including synthesis gas, from solid and liquid fuels, is given in Encyclopedia of Chemical Technology, Edited by Kirk-Othmer, Second Edition, Volume 10, pages 353-433, (1966), Interscience Publishers, New York, New York, the contents of which are herein incorporated by reference. The techniques for gasification of coal or other solid, liquid, or gaseous fuel are not considered to be a part of this invention.
It is considered desirable to effectively and more efficiently convert synthesis gas, and thereby coal and natural gas, to highly valued hydrocarbons such as motor gasoline with high octane number, petrochemical feedstocks, liquefiable petroleum fuel gas, and aromatic hydrocarbons. It is well known that synthesis gas will undergo conversion to form reduction products of carbon monoxide, such as hydrocarbons, at temperatures in the range of from about 300.degree. F. to about 850.degree. F. under pressures in the range of from about one to one thousand atmospheres pressure, over a fairly wide variety of catalysts. The Fischer-Tropsch process, for example, which has been most extensively studied, produces a range of products including liquid hydrocarbons, a portion of which have been used as low octane gasoline. The types of catalysts that have been studied for this and related processes included those based on metals or oxides of iron, cobalt, nickel, ruthenium, thorium, rhodium, and osmium.
The wide range of catalysts and catalysts modifications disclosed in the art and an equally wide range of conversion conditions for the reduction of carbon monoxide by hydrogen provide considerable flexibility toward obtaining selected boiling-range products. A review of the status of this art is given in "Carbon Monoxide-Hydrogen Reactions", Encyclopedia of Chemical Technology, Edited by Kirk-Othmer, Second Edition, Volume 4, pp. 446-488, Interscience Publishers, New York, New York, the text of which is incorporated herein by this reference. See also H. H. Storch, N. Golumbic & R. B. Anderson "The Fischer-Tropsch and Related Synthesis", John Wiley & Sons, Inc., New York, New York.
The hydrogenation of carbon oxides is highly exothermic and the various processes which involve this reaction must include means to remove the heat of reaction. These processes include Fischer-Tropsch synthesis, the Oxo process, methanation, methanol synthesis, and the like. It has been proposed to use liquid systems to aid in heat exchange. For example, that technique is utilized by the heavy slurry oil process and by the fused salt medium described in German Offenlegungsschrift No. 2603-892. According to the disclosure in the latter citation synthesis gas mixtures of hydrogen with oxides of carbon are reacted at temperatures above 500.degree. C. in a bath of molten alkali metal halides or carbonates in which is dispersed finely divided metal, metal oxides or carbides to produce methane.